Appurtenances is a term for what belongs to and goes with something else, with the appurtenance being less significant than what it belongs to. The word ultimately derives from Latin appertinere, "to appertain".

In Gestalt theory, appurtenance (or "belongingness") is the relation between two things seen which exert influence on each other. For example, fields of color exert influence on each other. "A field part x is determined in its appearance by its 'appurtenance' to other field parts. The more x belongs to the field part y, the more will its whiteness be determined by the gradient xy, and the less it belongs to the part z, the less will its whiteness depend on the gradient xz."[1]

In lexicology, an appurtenance is a modifier that is appended or prepended to another word to coin a new word that expresses "belongingness". In the English language, appurtenances are most commonly found in toponyms and demonyms, for example, 'Israeli', 'Bengali' etc. have an -i suffix of appurtenance.